Medicare Part B is enrollment-based, not automatic

Medicare Part B covers doctor visits, outpatient care, and medical equipment — but unlike Part A (hospital insurance), it does not start on its own. You have to sign up during a specific window, or you may face a permanent penalty on your premiums. Most people enroll when they turn 65, but the rules differ depending on whether you are still working and whether you have other health coverage.

The enrollment period that matters most is your Initial Enrollment Period (IEP), which runs for seven months: three months before the month you turn 65, the month you turn 65, and three months after. If you miss this window and do not have a valid reason, Medicare adds 10 percent to your Part B premium for each year you could have had it but did not.

Key Takeaways

  • You must sign up for Part B during your Initial Enrollment Period (seven months centered on your 65th birthday) or face a permanent premium increase.
  • If you are still working and covered by your employer's health plan, you may be able to delay Part B without penalty under the Special Enrollment Period rules.
  • You can enroll through Medicare.gov, by phone at 1-800-MEDICARE, or in person at your local Social Security office.
  • Part B coverage begins the first day of the month after you enroll, or the first day of the month you turn 65 if you enroll during your Initial Enrollment Period.

When your Initial Enrollment Period starts and ends

Your Initial Enrollment Period is a seven-month window. It begins three months before the month you turn 65. For example, if you turn 65 in June, your IEP starts in March. It ends three months after the month you turn 65, so in this example it would end in September.

If you enroll during this seven-month window, your coverage can start as early as the first day of the month you turn 65 (if you enroll in the month you turn 65 or earlier) or the first day of the following month (if you enroll after your birthday month). Enrolling early in your IEP gives Medicare time to process your request and send you a card before coverage begins.

Delaying Part B if you have employer coverage

If you are still working and your employer offers health insurance, you may not need Part B right away. Under the Special Enrollment Period (SEP) rules, you can delay Part B without penalty as long as you are covered by a group health plan through your current job or your spouse's current job.

The catch: you must enroll in Part B within eight months after your employment ends or your employer coverage stops, whichever comes first. If you miss that eight-month window, the same 10 percent annual penalty applies. When you do enroll, bring proof that you had employer coverage — your employer's benefits summary or a letter from your HR department works.

How to enroll in Part B

You have three main routes to enroll. The fastest is online at Medicare.gov. Go to the "Sign Up for Medicare" section, create or log into your Medicare account, and follow the prompts. You will need your Social Security number and information about any current health coverage.

You can also call 1-800-MEDICARE (1-800-633-4227) and speak to a representative. They can walk you through the process and answer questions about your specific situation. The line is open Monday through Friday, 8 a.m. to 8 p.m. Eastern time.

A third option is to visit your local Social Security office in person. You can find the nearest office at ssa.gov or by calling 1-800-772-1213. Bring your Social Security card, proof of citizenship or legal residency (passport, birth certificate, or naturalization papers), and proof of age. If you are still working, bring a recent pay stub or tax return to document your income.

What happens after you enroll

After you submit your enrollment, Medicare processes your request. You should receive a Medicare card in the mail within two to three weeks. Your Part B coverage begins on the first day of the month after you enroll, unless you enrolled during your Initial Enrollment Period in the month you turn 65 — in that case, coverage can start the first day of that month.

Your Part B premium is deducted from your Social Security check each month, or you receive a bill if you do not receive Social Security. The amount you pay depends on your income from two years ago; higher earners pay more. Medicare sends you a notice each year showing your premium for the coming year.

If you missed your Initial Enrollment Period

If you did not enroll during your seven-month Initial Enrollment Period and you do not have a valid reason (like employer coverage or a Special Enrollment Period circumstance), you can still enroll — but you will face a penalty. The penalty is 10 percent of the standard Part B premium for each full year you could have had Part B but did not.

You can enroll during the General Enrollment Period, which runs January 1 through March 31 each year. Coverage begins July 1 of that year. If you enroll after your Initial Enrollment Period, contact Medicare to explain your situation; in rare cases, they may waive the penalty if you have a valid reason for the delay.

Part B costs and what it covers

Part B has two costs: a monthly premium and a yearly deductible. The standard Part B premium and deductible amounts change each year. In 2024, the standard premium was $164.90 per month and the deductible was $240 per year, but these figures vary based on your income and change annually. Check Medicare.gov for the current year's amounts.

Part B covers doctor office visits, preventive care (like screenings and vaccines), outpatient surgery, mental health services, physical therapy, and durable medical equipment such as wheelchairs and oxygen. It does not cover dental, vision, or hearing care — those require separate coverage through a Medigap plan, a Medicare Advantage plan, or a standalone policy.

Frequently Asked Questions

What if I turn 65 while still working?

You can delay Part B without penalty if your employer has 20 or more employees and you are covered by their health plan. You have eight months after you leave that job to enroll in Part B without penalty. If your employer has fewer than 20 employees, you should enroll in Part B when you turn 65.

Can I change my mind after I enroll?

Yes, but only during specific windows. If you enroll and then change your mind, you can drop Part B, but you may face a penalty if you re-enroll later. Talk to Medicare before you drop coverage to understand the consequences for your situation.

Do I need Part B if I have a Medicare Advantage plan?

Yes. Medicare Advantage (Part C) is an alternative way to receive Part A and Part B benefits, but you must be enrolled in both Part A and Part B to use it. You cannot have Part C without Part B.

What if I am not a U.S. citizen?

You can enroll in Part B if you are a lawful permanent resident (green card holder) and have lived in the United States for at least five years. Bring proof of your legal residency status when you enroll.